(i) Field of the Invention
This invention relates to a re-entrable duct seal which protects against the passage of water through the duct and especially of the re-entrable duct seal for use with an environmentally-controlled manhole to protect against the passage of water and gas through the duct.
(ii) Description of the Prior Art
A re-entrable duct provided with a seal may be used in any instance where it is desired to penetrate a wall and yet provide a water-tight and preferably also a gas-tight re-entrable seal. In one preferred use, it is adapted for use on an environmentally-controlled manhole, which is a structure intended as an underground housing for electronic switching equipment. The duct seal is provided to allow telephone cable to enter the environmentally-controlled manhole without allowing ingress of water and also, preferably, of gas.
Current duct sealing methods have not been completely successful. Usually, sealing compounds are used to encapsulate cables in the conduits. The compounds typically take many hours to set up and often do not seal properly when placed in wet ducts. Such existing compounds often leak and are thus considered unacceptable for use in such environmentally-controlled manholes.